Signal converter and control device

ABSTRACT

A signal converter  100  includes, for at least two-phase signals detected by a resolver excited by a carrier signal having a carrier frequency fc, a first phase shifter  101  that shifts a phase of a first phase signal of the resolver with a pole at a frequency f 1  lower than the carrier frequency fc, a second phase shifter  102  that shifts a phase of a second phase signal of the resolver with a pole at a frequency f 2  higher than the carrier frequency fc, and a synthesizer  103  that combines the phase-shifted first phase signal with the phase-shifted second phase signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/159,840, filed on May 20, 2016, which is basedupon and claims the benefit of priority from Japanese patent applicationNo. 2015-154994, filed on Aug. 5, 2015, the disclosures of which areincorporated herein in their entirety by reference.

BACKGROUND

The present invention relates to a signal converter and a controldevice, and in particular, a signal converter and a control device usedfor controlling a motor.

As a rotation angle sensor, a resolver that detects a rotation angle ofa rotor based on fluctuations in a magnetic field caused by a rotationof the rotor has been known.

Japanese Unexamined Patent Application Publications No. H8-287173 andNo. H8-35856 disclose methods in which: the phase of one of two-phaseresolver signals obtained by one-phase excitation is shifted by 90° by asignal converter; the phase-shifted signal is combined with the other ofthe two-phase resolver signals; and the angle of the resolver isdetected from the combined signal. Further, Japanese Unexamined PatentApplication Publication No. 2004-347612 discloses a device that detects(i.e., determines), in the angle of a resolver, whether or not there isan abnormality in the angle detection.

SUMMARY

The present inventors have found the following problem. In thesemethods, there has been a problem that when the rotor of the resolverrotates, the phase shift by the phase shifter deviates from 90° andhence a large error occurs in the detected angle.

Further, as a technique for shifting the phase of a resolver signal, anRD (Resolver Digital) converter has been known. The RD converterperforms tracking by synchronously wave-detecting a signal synthesizedfrom two-phase output resolver signals and a carrier signal for excitingthe resolver, and feeding back a shift amount of the phase from thewave-detected signal. This RD converter requires a complicatedconfiguration and hence has a circuit size larger than the size of thoseused in the methods disclosed in the Japanese Unexamined PatentApplication Publications No. H8-287173 and No. H8-35856.

As described above, no signal converter having excellent detected-angleaccuracy and a small circuit size has been provided in the past.

Other objects and novel features will be more apparent from thefollowing description in the specification and the accompanyingdrawings.

A first aspect of the present invention is a signal converter thatshifts a phase of one of two-phase outputs of a resolver having acarrier frequency fc by an amount φ1 by using a phase shifter having apole f1, shifts a phase of the other of the two-phase outputs by anamount φ2 by using a phase shifter having a pole f2, in which the polesof the phase shifters satisfies a relation “f1<fc<f2”.

It is possible to provide a signal converter having excellentdetected-angle accuracy and a small circuit size.

According to the above-described aspect, it is possible to maintain aphase difference “φ2−φ1” at a constant angle of 90 degrees even when thefrequency varies in a range between “fc−Δ” and “fc+Δ” (Δ is afluctuation caused by the rotation speed of the rotor).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, advantages and features will be moreapparent from the following description of certain embodiments taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram showing a configuration of a signal converteraccording to an outline of an embodiment;

FIG. 2 is a block diagram showing a configuration of a signal converterand a control device according to a first embodiment;

FIG. 3 is a circuit diagram showing a configuration of a phase shifteraccording to the first embodiment;

FIG. 4 is a graph showing an example of a carrier signal and aphase-modulated signal;

FIG. 5 is a graph showing a phase difference between a clock signal of acarrier frequency and a shaped phase-modulated signal;

FIG. 6 is a graph showing a relation between frequencies detected by adetection coil of a resolve and phase shifts by a phase shifter in thesignal converter according to the first embodiment;

FIG. 7 is a graph showing a relation between frequencies detected by thedetection coil of the resolve and differences between phase shifts bytwo phase shifters in the signal converter according to the firstembodiment;

FIG. 8 is a graph for comparing a relation between frequencies detectedby a detection coil of a resolve and differences between phase shifts byphase shifters in the signal converter according to the first embodimentwith a relation between them in an all-pass filter;

FIG. 9 is a graph showing a relation between frequencies detected by thedetection coil of the resolve and differences between phase shifts bytwo phase shifters in the signal converter according to the firstembodiment;

FIG. 10 is a block diagram showing a configuration of a signal converterand a control device according to a second embodiment;

FIG. 11 is a block diagram showing a configuration of a signal converterand a control device according to a third embodiment; and

FIG. 12 is a flowchart showing an example of operations of the signalconverter and the control device according to the third embodiment.

DETAILED DESCRIPTION

For clarifying the explanation, the following descriptions and thedrawings may be partially omitted and simplified as appropriate.Further, each of the elements that are shown in the drawings asfunctional blocks for performing various processes can be implemented byhardware such as a CPU, a memory, and other types of circuits, orimplemented by software such as a program loaded in a memory. Therefore,those skilled in the art will understand that these functional blockscan be implemented solely by hardware, solely by software, or acombination thereof. That is, they are limited to neither hardware norsoftware. Note that the same symbols are assigned to the same componentsthroughout the drawings and duplicated explanations are omitted asrequired.

Outline of Embodiment

FIG. 1 is a block diagram showing a configuration of a signal converteraccording to an outline of an embodiment. In FIG. 1, a signal converter100 includes a first phase shifter 101, a second phase shifter 102, anda synthesizer 103. The signal converter 100 converts at least two-phasesignals output from a resolver excited at a carrier frequency fc andthereby makes the two-phase signals have a predetermined phasedifference therebetween.

The first phase shifter 101 shifts the phase of a first phase signal ofthe resolver with a pole at a frequency f1 lower than the carrierfrequency fc and outputs the phase-shifted first phase signal to thesynthesizer 103.

The second phase shifter 102 shifts the phase of a second phase signalof the resolver with a pole at a frequency f2 higher than the carrierfrequency fc and outputs the phase-shifted second phase signal to thesynthesizer 103.

The synthesizer 103 combines the phase-shifted first phase signal withthe phase-shifted second phase signal and externally outputs thesynthesized signal (i.e., combined signal).

As described above, the signal converter according to the outline of theembodiment shifts the phase of the first phase signal of the resolverwith the pole of the frequency f1 lower than the carrier frequency fc,shifts the phase of the second phase signal of the resolver with thepole of the frequency f2 higher than the carrier frequency fc, andcombines the phase-shifted first phase signal with the phase-shiftedsecond phase signal. As a result, it is possible to provide a signalconverter having excellent detected-angle accuracy and a small circuitsize.

First Embodiment

In a first embodiment, a detailed configuration of the signal converter100 explained above in the outline of the embodiment and a controldevice for a motor using the signal converter 100 are explained.

Firstly, a function of each component of a signal converter and acontrol device according to the first embodiment is explained. FIG. 2 isa block diagram showing a configuration of a control device according tothe first embodiment.

In FIG. 2, a control device 200 includes an analog circuit 300, acounter circuit 400, a microcomputer controller 500, and a power circuit600. Further, the control device 200 controls the rotation of a motor202 based on signals from a resolver 201. The rotor sections of theresolver 201 and the rotor section of the motor 202 are both fixed on acommon rotation shaft 203 and hence the resolver 201 and the motor 202rotate in a synchronized manner.

The resolver 201 further includes an excitation coil 204, a detectioncoil 205, and a detection coil 206. The excitation coil 204 is a coilthat generates a magnetic field by an electric signal supplied to theexcitation coil 204. The detection coils 205 and 206 are coils thatdetect fluctuations in the magnetic field and output the detectedfluctuations as an electric signal.

The excitation coil 204, the detection coil 205, and the detection coil206 are disposed in the stator section of the resolver 201 andfluctuations in the magnetic field are detected by the rotation of therotor section of the resolver 201. However, any device or structure thatcan detect fluctuations in a magnetic field by the rotation of a rotoras at least two-phase electric signals may be used as the resolver 201.For example, the excitation coil 204 may be disposed in the rotorsection and the detection coils 205 and 206 may be disposed in thestator section, and fluctuations in the magnetic field may be detectedby the rotation of the rotor section.

Further, the detection coils 205 and 206 are disposed with apredetermined angle therebetween, so that the detection coils 205 and206 detect a fluctuation in the magnetic field as signals havingmutually-different phases. For example, the detection coils 205 and 206are disposed with an angle of 90° therebetween, so that the detectioncoil 205 detects a fluctuation in the magnetic field as a sine wave andthe detection coil 206 detects it as a cosine wave.

Next, a configuration of the analog circuit 300 is explained. The analogcircuit 300 includes an excitation circuit 301, a phase shifter 101, aphase shifter 102, a band-pass filter 329, OP amplifiers OP302, OP315,OP320, OP327 and OP330, transistors TR303 and TR304, diodes D305 andD306, and resistors R311, R312, R313, R314, R316, R317, R318, R319,R325, R326 and R328.

The excitation circuit 301 generates a cosine-wave carrier signal havinga frequency fc, which is obtained by frequency-dividing a referenceclock signal, and outputs the generated carrier signal to the OPamplifier OP302.

The OP amplifier OP302, the push-pull-connected transistors TR303 andT304, and the diodes D305 and D306 amplify the carrier signal and outputthe amplified carrier signal to the excitation coil 204 of the resolver201.

The OP amplifier OP315 and the resisters R311, R312, R313 and R314 forma differential amplifier, and amplify a signal detected by the detectioncoil 205 and output the amplified signal to the phase shifter 101.Similarly, the OP amplifier OP320 and the resisters R316, R317, R318 andR319 form a differential amplifier, and amplify a signal detected by thedetection coil 206 and output the amplified signal to the phase shifter102.

The outputs of the phase shifters 101 and 102 are connected to eachother through the resistors R325 and R326, respectively, so that asignal that is obtained by modulating the phase of the carrier frequencyby the rotation angle of the rotor is provided. Details of the signalsynthesis are described later.

The OP amplifier OP 327 and the resistor R328 form an invertingamplifier circuit, and amplify the signal obtained by modulating thephase of the carrier frequency by the rotation angle of the rotor andoutput the amplified signal to the band-pass filter 329.

The band-pass filter 329 attenuates signal components of thephase-modulated signal outside a predetermined frequency range andoutputs the resultant signal to the OP amplifier OP330. Thepredetermined frequency range is, for example, a frequency range inwhich the carrier frequency can be changed according to the rotationspeed of the rotor.

The OP amplifier OP330 forms a comparator, and shapes thephase-modulated signal into a square wave and outputs the shaped signalto a CLK synchronization circuit 403.

Next, a configuration of the counter circuit 400 is explained. Thecounter circuit 400 includes a reference CLK circuit 401, an excitationCLK circuit 402, a phase difference counter 404, and the CLKsynchronization circuit 403.

The reference CLK circuit 401 generates a signal having a referencefrequency and outputs the generated reference clock signal to theexcitation CLK circuit 402, the phase difference counter 404, and theCLK synchronization circuit 403.

The excitation CLK circuit 402 divides the frequency of the referenceclock signal generated by the reference CLK circuit 401 and therebyoutputs a clock signal having a carrier frequency, which is obtained bythe frequency-division, to the excitation circuit 301 and the phasedifference counter 404.

The CLK synchronization circuit 403 synchronously wave-detects theshaped phase-modulated signal and the shaped carrier signal and outputsthe wave-detected signal to the phase difference counter 404 and aposition calculator 501.

The phase difference counter 404 counts (or measures) a phase differenceobtained by the synchronous wave-detection with the resolution of thereference frequency and outputs the count result to the positioncalculator 501 and a three-phase converter 509.

Next, a configuration of the microcomputer controller 500 is explained.The microcomputer controller 500 includes the position calculator 501, aserial communication unit 502, a subtracter 503, a position gaincalculator 504, a differential process unit 505, a subtracter 506, aspeed gain calculator 507, a torque calculator 508, the three-phaseconverter 509, and multipliers 510, 511 and 512.

The position calculator 501 calculates a position detection value fromthe wave-detected signal and the count result of the phase differenceand outputs the calculated position detection value to the subtracter503 and the differential process unit 505.

The serial communication unit 502 receives an external position commandsignal and outputs the received position command signal to thesubtracter 503. The subtracter 503 subtracts the position command signalfrom the position detection value and outputs the obtained positiondeviation to the position gain calculator 504.

The position gain calculator 504 calculates the target speed of themotor 202 by multiplying the position deviation by a predeterminedposition gain. The differential process unit 505 calculates the rotationspeed of the motor 202 by differentiating a detected signal representingthe rotational position. The subtracter 506 subtracts the speeddetection value from the target speed and outputs the obtained speeddeviation to the speed gain calculator 507.

The speed gain calculator 507 calculates a torque command value bymultiplying the speed deviation by the speed gain. The torque calculator508 calculates current command values representing currents that shouldbe fed to the respective phases of the motor 202 from the torque commandvalue. The three-phase converter 509 generates three-phase signals fromthe count result of the phase difference and outputs the generatedthree-phase signals to the respective multipliers 510, 511 and 512.

The multipliers 510, 511 and 512 generate three-phase control signals bymultiplying the respective current command values by the three-phasesignals and output the generated three-phase control signals to thepower circuit 600. The power circuit 600 is an inverter that performsthree-phase PWM (Pulse Width Modulation) control for the motor 202 basedon the three-phase control signals.

With the above-described configuration, the control device 200 detectsthe rotation angle of the rotor and controls the motor. However, itshould be noted that any configuration capable of shifting a phase canbe used as each of the phase shifters 101 and 102, which are componentsdisposed in the control device 200. For example, an all-pass filterusing an OP amplifier is a preferred configuration capable of shifting aphase. This phase shifter using an OP amplifier is explained withreference to FIG. 3. FIG. 3 is a circuit diagram showing a configurationof a phase shifter according to the first embodiment. In FIG. 3, thephase shifter 101 includes an OP amplifier OP701, resistors R702 andR703, and a capacitor C705.

A signal output from the detection coil 205 of the resolver 201 is inputto the inverting input terminal of the OP amplifier OP701 through theresistor R702 and also input to the non-inverting input terminal of theOP amplifier OP701 through the resistor R703. Further, the non-invertinginput terminal of the OP amplifier OP701 is connected to the groundthrough the capacitor C705. Further, the output terminal of the OPamplifier OP701 is connected to the inverting input terminal of the OPamplifier OP701.

With the above-described configuration, the phase shifter 101 forms anall-pass filter using an OP amplifier. A similar configuration can beused for the phase shifter 102.

The phase shift and the pole can be determined by the transfer functionof the all-pass filter. Therefore, the impedance of the resistor R703and the capacitance of the capacitor C705 are determined based on adesired phase shift and a desired pole.

Note that the difference between the phase shifts of the phase shifters101 and 102 can be adjusted to 90° by adjusting the carrier frequencyfc, the frequency f1 of the pole of the phase shifter 101, and thefrequency f2 of the pole of the phase shifter 102 so that they satisfyrelations “f1=fc/n” and “f2=fc×n” (n is an arbitrary positive realnumber).

For example, by adjusting the impedance of each of the resistors R702,R703 and R704 to 100 kΩ and adjusting the capacitance of the capacitorC705 to 80 pF, the frequency f1 can be adjusted to 1.99 kHz (f1=1.99kHz). Further, by adjusting the impedance of each of the resistors R702,R703 and R704 to 100 kΩ and adjusting the capacitance of the capacitorC705 to 135 pF, the frequency f2 can be adjusted to 11.8 kHz (f1=11.8kHz).

When the carrier frequency fc is 4.88 kHz (fc=4.88 kHz), theabove-described frequencies f1 and f2 (f1=1.99 kHz, f2=11.8 kHz) satisfythe relations “f1=fc/n” and “f2=fc×n” (n is an arbitrary positive realnumber). Therefore, the difference between the phase shifts of the phaseshifters 101 and 102 becomes 90°.

Next, a process for detecting a rotation angle is explained withreference to FIG. 2. Firstly, a carrier signal generated by theexcitation circuit 301 is amplified by the OP amplifier OP302 and thetransistors TR303 and TR304, and the amplified carrier signal is inputto the excitation coil 204.

The magnetic field generated by the excitation coil 204 fluctuates dueto the rotation of the rotor section of the resolver 201. Then, thefluctuations in the magnetic field are detected by the detection coils205 and 206.

For example, when the excitation coil 204 is one-phase-excited by acarrier signal having a sine wave sin ωt and two-phase output signalsdetected by the detection coils 205 and 206 are amplified, the amplifiedtwo-phase output signals X1 and X2 are defined as follows.

X1=K·sin θm×sin ωt

X2=K·cos θm×sin ωt

In the above-shown expressions: ω is the angular momentum of the carriersignal; t is a time; θm is the rotation angle of the rotor of theresolver 201; and K is the gain of the OP amplifiers OP315 and OP317.

Here, when the phase shifts of the phase shifters 101 and 102 arerepresented by φ1 and φ2, respectively, and an all-pass filter is usedfor each of the phase shifters 101 and 102, the signal converter 100 canbe designed so that a relation “φ1−φ2=−90°” is satisfied. For example,by adjusting the frequencies of the poles of the phase shifters 101 and102 to 1.99 kHz and 11.8 kHz, respectively, for the carrier frequency fcof 4.88 kHz (fc=4.88 kHz), the relation “φ1−φ2=−90°” can be satisfied.

Further, the filtered signals in the phase shifters 101 and 102 aredefined as follows.

X1=K·sin θm×sin(ωt−φ1)

X2=K·cos θm×sin(ωt−φ2)

Here, the following relation can be derived from the relation“−φ2=−φ1−90°”.

$\begin{matrix}{{X\; 2} = {{K \cdot \cos}\; \theta \; m \times {\sin ( {{\omega \; t} - {\phi 1} - {90{^\circ}}} )}}} \\{= {{{- K} \cdot \cos}\; \theta \; m \times {\cos ( {{\omega \; t} - {\phi 1}} )}}}\end{matrix}$

In the synthesizer 103, the signals X1 and X2, which are phase-shiftedin the phase shifters 101 and 102, are combined with each other. Here,the following relation can be derived by adding X1 and X2.

$\begin{matrix}{Y = {{X\; 1} + {X\; 2}}} \\{= {{{K \cdot \sin}\; \theta \; m \times {\sin ( {{\omega \; t} - {\phi 1}} )}} - {{K \cdot \cos}\; \theta \; m \times {\cos ( {{\omega \; t} - {\phi 1}} )}}}} \\{= {{- K} \cdot {\cos ( {{\omega \; t} - {\phi 1} + {\theta \; m}} )}}}\end{matrix}$

That is, a signal that is obtained by modulating the phase of thecarrier frequency (angular frequency) ω by the rotation angle θm of therotor is provided. FIG. 4 is a graph showing an example of the carriersignal and the phase-modulated signal. In FIG. 4, the vertical axisindicates amplitudes and the horizontal axis indicates time. As shown inFIG. 4, the carrier signal and the phase-modulated signal are signalshaving the same frequency and different phases. Therefore, it ispossible to calculate the rotation angle of the rotor based on the phasedifference between the carrier signal and the phase-modulated signal.

An example of a preferred method is a method in which thephase-modulated signal is shaped into a square wave and the phasedifference between the shaped phase-modulated signal and the clocksignal having the carrier frequency is detected. FIG. 5 is a graphshowing a phase difference between the clock signal having the carrierfrequency and the shaped phase-modulated signal. In FIG. 5, the verticalaxis indicates amplitudes and the horizontal axis indicates time. Asshown in FIG. 5, there is a phase difference between the clock signalhaving the carrier frequency and the shaped phase-modulated signal,which corresponds to the rotation angle of the rotor.

In the CLK synchronization circuit 403, a wave-detected signal isobtained by synchronizing the signal that is obtained by modulating thephase of the carrier frequency co by the rotation angle θm of the rotorwith the clock signal having the carrier frequency.

The motor is controlled based on the obtained detected signal in themicrocomputer controller 500 and the power circuit 600.

Next, the accuracy of the rotation angle, which is detected through theabove-described series of processes, is explained. As described above,the rotation angle θm of the rotor is obtained by adjusting the phaseshifts φ1 and φ2 in the phase shifters 101 and 102, respectively, sothat the relation “φ1−φ2=−90°” (or “φ1−φ2=90°”) is satisfied.

Therefore, the farther the value “φ1−φ2” deviates from −90°, the largerthe error of the detected angle becomes. Further, the closer the value“φ1−φ2” is to −90°, the smaller the error of the detected angle becomes.

That is, it is possible to accurately detect the rotation angle of therotor by maintaining the difference between the phase shifts by the twophase shifters at −90° even when the frequency of the two-phase outputsignals from the resolver changes due to the rotation speed of therotor.

FIG. 6 is a graph showing a relation between frequencies detected by thedetection coils of the resolve and the phase shifts by the phaseshifters in the signal converter according to the first embodiment. InFIG. 6, the horizontal axis indicates the frequency (Hz) of thetwo-phase output signals detected by the detection coils 205 and 206,and the vertical axis indicates the phase shifts (degrees) by the phaseshifters. As shown in FIG. 6, the phase shifter 101 has its pole at afrequency of 1.99 kHz (f1=1.99 kHz) and the phase shifter 102 has itspole at a frequency of 11.8 kHz (f2=11.8 kHz).

In the first embodiment, the difference between the phase shifts by thetwo phase shifters is maintained roughly at −90°. FIG. 7 is a graphshowing a relation between frequencies detected by the detection coilsof the resolve and the difference between the phase shifts by the twophase shifters in the signal converter according to the firstembodiment. In FIG. 7, the horizontal axis indicates the frequency (Hz)of the two-phase output signals detected by the detection coils 205 and206, and the vertical axis indicates the phase shifts (degrees) by thetwo phase shifters.

As shown in FIG. 7, the difference between the phase shifts by the twophase shifters is maintained roughly at −90° in a range of 4.88 kHz±1kHz.

Here, a difference between fluctuations in the two phase shifters andthose in one all-pass filter is explained. FIG. 8 is a graph forcomparing a relation between frequencies detected by the detection coilsof the resolve and differences between phase shifts by the phaseshifters in the signal converter according to the first embodiment witha relation between them in one all-pass filter. In FIG. 8, thehorizontal axis indicates the frequency (Hz) of the two-phase outputsignals detected by the detection coils 205 and 206, and the verticalaxis indicates the phase shifts (degrees).

As shown in FIG. 8, in the case where one all-pass filter is used, whenthe carrier frequency shifts by 1 kHz from 4.88 kHz, the phase shiftchanges from −90° to −100°, i.e., changes by 10°. In contrast to this,in the first embodiment, when the frequency of the two-phase outputsignals from the resolver shifts by 1 kHz from 4.88 kHz, i.e., from thecarrier frequency, the change in the phase shift from −90° is no morethan 1°.

As described above, the signal converter according to the firstembodiment can maintain the difference between the phase shifts by thetwo phase shifters at −90° even when the frequency of the two-phaseoutput signals from the resolver changes due to the rotation of therotor and hence can accurately detect the rotation angle of the rotor.

Further, the signal converter according to the first embodiment does notrequire the circuit that feeds back the phase difference and correctsthe phase difference, which is required in the tracking method, thusmaking it possible to reduce the circuit size.

Further, in the signal converter according to the first embodiment,there is no need to feed back the phase difference and correct the phasedifference, which is required in the tracking method, thus making itpossible to detect the position in a shorter time than that in thetracking method.

Further, the signal converter according to the first embodiment caninclude a band-pass filter that lets the phase-modulated signal passtherethrough in a frequency range in which the carrier frequency ischanged according to the rotation speed of the rotor and thereby removethe drive current noise caused by the magnetic circuit of the motor andthe PWM modulation noise of the inverter, thus making it possible toachieve an accurate signal conversion.

Further, since the signal converter according to the first embodiment issimple and its circuit size is small, the interface between the signalconverter and a microcomputer can be easily constructed. Therefore, byincorporating the signal converter according to the first embodimentinto a microcomputer device, it is possible to improve the accuracy of abrushless motor, reduce the price thereof, and reduce the size thereof.

Note that the difference “φ1−φ2” between the phase shifts by the twophase shifters may be roughly 90° (i.e., does not have to be exactly90°), provided that it is in the range of the permissible error in thedetection of the rotation angle of the rotor. FIG. 9 is a graph showinga relation between frequencies detected by the detection coils of theresolve and differences between the phase shifts by the two phaseshifters in the signal converter according to the first embodiment. InFIG. 9, the horizontal axis indicates the frequency (Hz) of thetwo-phase output signals detected by the detection coils 205 and 206,and the vertical axis indicates the phase shifts (degrees) by the twophase shifters.

In FIG. 9, an example where the phase shift by the phase shifter 102 ischanged and the difference “φ1−φ2” between the phase shifts by the twophase shifters is thereby changed from −88° to −92° is shown. When thefrequency of the two-phase output signals from the resolver shifts by 1kHz from 4.88 kHz, i.e., from the carrier frequency, the change in thephase shift from −90° is no more than 2°. That is, the error in thephase shift is one fifth of that in the example where one all-passfilter is used.

Therefore, the value of the difference “φ1−φ2” may be roughly −90°(i.e., does not have to be exactly −90°. Specifically, the value of thedifference “φ1−φ2” is considered to be roughly −90° even when it is anyvalue in a range of −88° to −92°, and it is considered to be practicallyaccurate enough for the detection of the rotation angle of the rotor.

Note that the difference “φ1−φ2” means a relative difference between thetwo phases. Therefore, −90° and 90° are practically the same as eachother except for their expressions which are changed according to theorder of the two phases. That is, either of them can be applied,provided that they mean the same phase difference. This also holds truefor the case where the difference “φ1−φ2” is in the range of −88° to−92°.

Second Embodiment

In a second embodiment, an example in which four-phase coils are used inthe resolver is explained. FIG. 10 is a block diagram showing aconfiguration of a signal converter and a control device according tothe second embodiment.

In FIG. 10, the same reference numbers as those in FIG. 2 are assignedto the same components as those in FIG. 2, and their explanations areomitted. In FIG. 10, a control device 800 includes coils 801, 802, 803and 804, and resistors R811, R812, R813 and R814.

The excitation circuit 301 generates a cosine-wave carrier signal havinga frequency fc, which is obtained by frequency-dividing a referenceclock signal, and outputs the generated carrier signal to the OPamplifier OP302. The OP amplifier OP302, the push-pull-connectedtransistors TR303 and T304, and the diodes D305 and D306 amplify thecarrier signal and output the amplified carrier signal to the coils 801,802, 803 and 804 of the resolver 201.

One end of the coil 801 is connected to the output of an amplifiercircuit formed by the OP amplifier OP302 and the push-pull-connectedtransistors TR303 and T304 and the other end of the coil 801 isconnected to the inverting input terminal of the OP amplifier OP315.

Further, one end of the coil 803 is connected to the output of theamplifier circuit formed by the OP amplifier OP302 and thepush-pull-connected transistors TR303 and T304 and the other end of thecoil 803 is connected to the non-inverting input terminal of the OPamplifier OP315.

The OP amplifier OP315 forms a differential amplifier thatdifferentially-amplifies the outputs of the 0-phase coil 801 and the180-phase coil 803.

Similarly, one end of the coil 802 is connected to the output of theamplifier circuit formed by the OP amplifier OP302 and thepush-pull-connected transistors TR303 and T304 and the other end of thecoil 802 is connected to the inverting input terminal of the OPamplifier OP320.

Further, one end of the coil 804 is connected to the output of theamplifier circuit formed by the OP amplifier OP302 and thepush-pull-connected transistors TR303 and T304 and the other end of thecoil 804 is connected to the non-inverting input terminal of the OPamplifier OP320.

The OP amplifier OP320 forms a differential amplifier thatdifferentially-amplifies the outputs of the 90-phase coil 802 and the270-phase coil 804.

As describe above, the signal converter and the control device accordingto the second embodiment can accurately detect the rotation angle of therotor by using the four-phase coils.

Third Embodiment

If the winding in the resolver is not uniform, a carrier signal having afixed phase remains in the phase-modulated signal as a carrier errorcomponent, thus becoming a significant cause for a position error. In athird embodiment, an example in which the noise caused by the carriersignal is removed is explained.

When no carrier component is included in the value “X1+X2” obtained bycombining the two-phase signals of the resolver, the speed is constant.When a carrier component is included in the aforementioned value due toan error of the winding of the resolver or the like, an AC (AlternatingCurrent) fluctuation component is superposed on the speed. The speedincluding the fluctuation component is called a “speed ripple Vr”.

FIG. 11 is a block diagram showing a configuration of a signal converterand a control device according to the third embodiment. In FIG. 11, thesame reference numbers as those in FIG. 2 are assigned to the samecomponents as those in FIG. 2, and their explanations are omitted. InFIG. 11, a control device 900 includes a speed ripple calculator 901, acarrier amplitude phase correcting unit 902, a D/A (Digital/Analog)converter 903, and a resistor R904.

The speed ripple calculator 901 calculates a ripple component from adifferential value of the detected signal indicating the rotationalposition calculated by the differential process unit 505 and outputs thecalculated ripple component to the carrier amplitude phase correctingunit 902.

The carrier amplitude phase correcting unit 902 generates a correctionsignal and outputs the generated correction signal to the D/A converter903. Further, the carrier amplitude phase correcting unit 902arbitrarily changes the phase and the amplitude of the correction signalso that the ripple component is minimized. The operation for changingthe phase and the amplitude of the correction signal is described later.

The D/A converter 903 converts the digital correction signal into ananalog signal and outputs the analog correction signal to the invertinginput terminal of the OP amplifier OP327 through the resistor R904.

That is, a signal that is obtained by superposing the outputs of thephase shifters 101 and 102 and the output of the D/A converter 903 oneach other is input to the inverting input terminal of the OP amplifierOP327.

Next, operations of the signal converter and the control deviceaccording to the third embodiment are explained. FIG. 12 is a flowchartshowing an example of operations of the signal converter and the controldevice according to the third embodiment.

Firstly, in a step S1001, the motor 202 is continuously rotated at aconstant speed and the process proceeds to a step S1002.

In the step S1002, initial values for the amplitude ε and the phase Δare set in the carrier amplitude phase correcting unit 902 and theprocess proceeds to a step S1003.

In the step S1003, a carrier correction signal is generated with theamplitude ε and the phase Δ in the carrier amplitude phase correctingunit 902 and the process proceeds to a step S1004.

In the step S1004, it is determined whether or not the speed ripple Vris the minimum for the phase Δ in the speed ripple calculator 901. Whenthe speed ripple Vr is not the minimum for the phase Δ, the processproceeds to a step S1005, whereas when the speed ripple Vr is theminimum for the phase Δ, the process proceeds to a step S1006.

In the step S1005, the phase Δ is changed in the carrier amplitude phasecorrecting unit 902 and the process returns to the step S1003.

In the step S1006, it is determined whether or not the speed ripple Vris the minimum for the amplitude ε in the speed ripple calculator 901.When the speed ripple Vr is not the minimum for the amplitude ε, theprocess proceeds to a step S1007, whereas when the speed ripple Vr isthe minimum for the amplitude ε, the process proceeds to a step S1009.

In the step S1007, the amplitude ε is changed in the carrier amplitudephase correcting unit 902 and the process proceeds to the step S1008.

In the step S1008, a carrier correction signal is generated with theamplitude ε and the phase Δ in the carrier amplitude phase correctingunit 902 and the process returns to the step S1006.

In the step S1009, a carrier correction signal is generated whilekeeping the amplitude ε and the phase Δ at fixed values in the speedripple calculator 901 and the process for setting the amplitude ε andthe phase Δ is finished.

The above-described operation is a calibration operation performed atwhen the product is shipped, and hence may be performed only once.Therefore, the values set for the phase Δ and the amplitude ε may bestored in a nonvolatile memory included in the microcomputer controller500. Further, the above-described operation may be performed after theshipment. For example, the above-described operation may be performedduring the initialization operation upon the power-up or the like.

As described above, the signal converter and the control deviceaccording to the third embodiment can remove the noise caused by thecarrier signal of the resolver by generating a correction signal thatcancels out the ripple component caused by the carrier signal, searchingfor a phase and an amplitude for the correction signal by which theripple component is minimized, and superposing the correction signal onthe phase-modulated signal.

Note that in each of the above-described embodiments, the countercircuit 400 and the microcomputer controller 500 can be implemented byhardware such as an ASIC (Application Specific Integrated Circuit) orsoftware. Further, a part of the process may be implemented by softwareand the rest of the process may be implemented by hardware. When theprocess is implemented by software, a program(s) related to functionalblock processes may be executed in a computer system including one or aplurality of CPUs (Central Processing Units) such as a microprocessor.

Further, the above-described program can be stored in various types ofnon-transitory computer readable media and thereby supplied tocomputers. The non-transitory computer readable media includes varioustypes of tangible storage media. Examples of the non-transitory computerreadable media include a magnetic recording medium (such as a flexibledisk, a magnetic tape, and a hard disk drive), a magneto-optic recordingmedium (such as a magneto-optic disk), a CD-ROM (Read Only Memory), aCD-R, and a CD-R/W, and a semiconductor memory (such as a mask ROM, aPROM (Programmable ROM), an EPROM (Erasable PROM), a flash ROM, and aRAM (Random Access Memory)). Further, the program can be supplied tocomputers by using various types of transitory computer readable media.Examples of the transitory computer readable media include an electricalsignal, an optical signal, and an electromagnetic wave. The transitorycomputer readable media can be used to supply programs to computerthrough a wire communication path such as an electrical wire and anoptical fiber, or wireless communication path.

The present invention made by the inventors has been explained above ina specific manner based on embodiments. However, the present inventionis not limited to the above-described embodiments, and needless to say,various modifications can be made without departing from the spirit andscope of the present invention.

For example, each of the carrier frequency and the phase shift is notlimited to the values in the above-described embodiments.

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention can bepracticed with various modifications within the spirit and scope of theappended claims and the invention is not limited to the examplesdescribed above.

Further, the scope of the claims is not limited by the embodimentsdescribed above.

Furthermore, it is noted that, Applicant's intent is to encompassequivalents of all claim elements, even if amended later duringprosecution.

What is claimed is:
 1. A signal converter comprising: an excitationcircuit that generates a carrier signal having a carrier frequency tooutput the carrier signal to a rotation angle sensor: a first phaseshifter circuit that receives a first phase signal from the rotationangle sensor and shifts a phase of the first phase signal with a pole ata first frequency lower than the carrier frequency; a second phaseshifter circuit that receives a second phase signal from the rotationangle sensor and shifts a phase of the second phase signal with a poleat a second frequency higher than the carrier frequency; and asynthesizer circuit that combines the phase-shifted first phase signalwith the phase-shifted second phase signal and outputs a phase-modulatedsignal where the carrier signal is phase-modulated by a rotation angleof the rotation angle sensor.
 2. The signal converter according to claim1, wherein each of the first phase shifter circuit and the second phaseshifter circuit comprises an all-pass filter.
 3. The signal converteraccording to claim 1, wherein the first frequency is one Nth of thecarrier frequency and the second frequency is N times of the carrierfrequency (N is an arbitrary positive real number).
 4. The signalconverter according to claim 1, wherein a difference between a firstphase shifted by the first phase shifter circuit and a second phaseshifted by the second phase shifter circuit is roughly 90°.
 5. Thesignal converter according to claim 1, further comprising: a band-passfilter that attenuates, for the phase-modulated signal, a signalcomponent outside a predetermined frequency range centered on thecarrier frequency.
 6. A signal converter comprising: an excitationcircuit that generates a carrier signal having a carrier frequency tooutput the carrier signal to a rotation angle sensor: a first phaseshifter circuit that shifts a phase of the first combined signal basedon a first and second phase signal from the rotation angle sensor with apole at a first frequency lower than the carrier frequency; a secondphase shifter circuit that shifts a phase of the second combined signalbased on a third and a fourth phase signal from the rotation anglesensor with a pole at a second frequency higher than the carrierfrequency; and a synthesizer circuit that combines the phase-shiftedfirst combined signal with the phase-shifted second combined signal andoutputs a phase-modulated signal where the carrier signal isphase-modulated by a rotation angle of the rotation angle sensor,wherein the first and the second phase signals have phases differentfrom each other by roughly 180°, wherein the third and the fourth phasesignals have phases different from each other by roughly 180°, andwherein the first and the third phase signals have phases different fromeach other by roughly 90°.
 7. The signal converter according to claim 1,further comprising: a signal generator that generates a correctionsignal for cancelling out a ripple component caused by the carriersignal, wherein the synthesizer superposes the correction signal on thephase-modulated signal.
 8. The signal converter according to claim 1,further comprising: a synchronization circuit that synchronouslywave-detects the phase-modulated signal at the carrier frequency fc andoutputs a synchronously wave-detected signal; a speed ripple calculatorthat calculates a ripple component based on a differential value of thesynchronously wave-detected signal from the synchronization circuit; anda carrier amplitude phase correction unit that generates a correctionsignal with a phase and an amplitude by which the ripple component isminimized, wherein the synthesizer superposes the correction signal onthe phase-modulated signal.
 9. A control device for a motor, comprising:an excitation circuit that generates a carrier signal having a carrierfrequency to output the carrier signal to a rotation angle sensor: afirst phase shifter circuit that receives a first phase signal from therotation angle sensor and shifts a phase of the first phase signal witha pole at a first frequency lower than the carrier frequency; a secondphase shifter circuit that receives a second phase signal from therotation angle sensor and shifts a phase of the second phase signal witha pole a second frequency higher than the carrier frequency; asynthesizer circuit that combines the phase-shifted first phase signalwith the phase-shifted second phase signal and outputs a phase-modulatedsignal where the carrier signal is phase-modulated by a rotation angleof the rotation angle sensor; a synchronization circuit thatsynchronously wave-detects the phase-modulated signal at the carrierfrequency fc and outputs a synchronously wave-detected signal; and acontroller that controls the motor based on the synchronouslywave-detected signal.
 10. The control device according to claim 9,wherein the first phase shifter circuit shifts a phase of a firstcombined signal based on the first phase signal and a third phase signalfrom the rotation angle sensor, the first and the third phase signalshaving phases different from each other by roughly 180°, and the secondphase shifter circuit shifts a phase of a second combined signal basedon the second signal and a fourth signal from the rotation angle sensor,the second and the fourth phase signals having phases different fromeach other by roughly 180°.
 11. The control device according to claim 9,further comprising: a signal generator that generates a correctionsignal for cancelling out a ripple component causes by the carriersignal, wherein the synthesizer superposes the correction signal on thephase-modulated signal.